The present invention relates to a solid-state imaging device such as a CCD (charge-coupled device) solid-state imaging device or the like and a manufacturing method thereof and a semiconductor device manufacturing method such as a process for forming a metal interconnection, a process for burying a contact-hole or the like.
Generally, in solid-state imaging devices, after electrical components such as charge-transfer regions, channel-stop regions, photo-sensor regions, gate electrodes and so on were formed, a metal film for preventing light from becoming incident on other regions than a photo-sensor region is formed as a light-shielding film.
In conventional solid-state imaging devices, metal thin films such as aluminum, tungsten, tungsten silicide and so on deposited by sputtering have heretofore been used as the light-shielding film. The light-shielding film that was deposited by sputtering is processed by photo-etching to selectively remove the above-mentioned photo-sensor portion only, thereby resulting in pixels of the solid-state imaging device being formed.
However, if the above-mentioned light-shielding film has a poor light-shielding characteristic, i.e. light passes other regions than the photo-sensor region, then light becomes incident on a so-called optical black portion or a phenomenon called a smear in which light is leaked into a charge transfer portion occurs.
If the light-shielding film is thick, then it becomes difficult to process the light-shielding film by microminiaturization or a dark current in the device increases and a point defect increases due to damages caused on the underlayer upon dry etching.
Moreover, if the light-shielding film cannot be reduced in thickness as a size of a pixel is reduced, then a length from an on-chip micro lens to the surface of the photo-sensor increases to lower a lens focusing efficiency of the on-chip micro lens and to thereby lower a photo-sensor sensitivity.
On the other hand, the metal film deposited by sputtering is poor in step coverage and an effective film thickness of a side wall of a step is reduced so that light passes the metal film. Therefore, the film thickness of the metal film cannot be reduced so much. In particular, a leakage of light into the aluminum thin film from a grain boundary is remarkable, and hence the film thickness of the aluminum thin film cannot be decreased up to less than 400 nm.
Since the metal thin film, in particular, the tungsten thin film deposited by a CVD (chemical vapor deposition) which is widely used in the manufacturing process of semiconductors has a considerably satisfactory step coverage in principle, the tungsten film is very effective as the light-shielding film for solid-state imaging devices. However, the tungsten film cannot be directly deposited on a silicon oxide film and is extremely low in adhesion so that an adhesion layer is indispensable for the tungsten film when the tungsten film is deposited on the silicon oxide film. As the adhesion layer, there has hitherto been used a titanium nitride film.
However, since a titanium system material such as a TiN (titanium nitride) film has a function to adsorb hydrogen, the supply of hydrogen from an upper layer to reduce an interface state density of a substrate surface is hindered and the interface state density remains, thereby resulting in a dark current being increased.
Therefore, the titanium material is not suitable as the material of the light-shielding film of the solid-state imaging device.
Since the size of a pixel in a CCD is reduced as a camera is miniaturized recently, there is an increasing demand for a light-shielding film which is strong against the transmission of light and which may be reduced in thickness.
In view of the aforesaid aspect, it is an object of the present invention to provide a solid-state imaging device and a manufacturing method thereof in which a sensitivity may be prevented from being lowered and a smear may be suppressed as a pixel size is reduced and in which an excellent image quality may be obtained even though the solid-state imaging device is miniaturized.
It is another object of the present invention to provide a method of manufacturing a semiconductor device in which a conductive layer having an excellent adhesion with an underlayer and whose surface has an excellent flatness is formed in the process for forming a metal interconnection and the process for burying a contact-hole.
According to a first aspect of the present invention, there is provided a solid-state imaging device having a light-receiving portion formed on a semiconductor substrate and a light-shielding film formed so as to cover an electrode formed on the semiconductor substrate at least on its regions other than a region above the light-receiving portion. This solid-state imaging device is arranged such that the light-shielding film has a multilayer structure including a first film formed of a film deposited by sputtering or vapor deposition and a second film deposited by chemical vapor deposition.
According to a second aspect of the present invention, there is provided a method of manufacturing a solid-state imaging device which comprises the steps of forming a light-receiving portion on a semiconductor substrate, forming an electrode on the semiconductor substrate at least on its regions other than a region above the light-receiving portion, forming an insulating film on the electrode, and forming a light-shielding film so as to cover the insulating film, wherein the light-shielding film is formed in such a manner that, after a first film is formed by sputtering or vapor deposition, a second film is formed on the first film by chemical vapor deposition.
According to a third aspect of the present invention, there is provided a method of manufacturing a semiconductor device which comprises the steps of forming a first film on the surface of a substrate by sputtering or vapor deposition, removing a native oxide from the surface of the first film, forming a second film on the first film by chemical vapor deposition, and forming a conductive film of a mulitlayer film including the first film and the second film.
According to the solid-state imaging device of the present invention, since the first film is formed of the film deposited by sputtering or vapor deposition, the first film has an excellent adhesion with the underlayer. Also, since the second film formed of the tungsten film deposited by chemical vapor deposition is formed on the first film, the second film is formed with an excellent adhesion through the first film, and a sufficient light-shielding property may be maintained by the second film.
According to the method of manufacturing a solid-state imaging device of the present invention, since the first film is formed of the film deposited by sputtering or vapor deposition, the first film is deposited with an excellent adhesion with the underlayer. Also, since the second film formed of the tungsten film is formed on the first film, the second film is formed with an excellent adhesion through the first film. Also, since the second film is deposited by chemical vapor deposition, a step coverage is satisfactory and a leakage of light from a step side wall or the like may be prevented, thereby making is possible to maintain a sufficient light-shielding property.
According to the method of manufacturing a semiconductor device of the present invention, after the first film was formed, the natural oxide is removed from the surface of the first film and then the second film is formed. Thus, the surface of the first film may be made flat, and the surface of the second film also may be formed satisfactorily.